Many heat transfer situations combine conduction, convection and radiation mechanisms. One such situation commonly encountered is that of an uncovered window through which the sun's radiant energy enters. There is a heat flux inward which depends on the intensity of the sunlight and the angle of the sun. Reflection increases as the sun direction angle increases away from that normal to the surface of the glass. The intensity changes with the weather. Therefore, there is no way of predicting the heat flux in through the window by radiant heat transfer.
When the weather is cold outside, heat will be lost through a window by radiation and convection also. The convection loss is complex. It involves heat transfer by convection on the inside surface, heat transfer by conduction through the glass, and heat transfer by convection on the outside surface.
When it is warmer outside than inside the window, as in the summer, heat will usually be transferred inwards by all the heat transfer mechanisms. It would be possible to close the window with a thermal barrier such as insulating blinds, covers, or shutters to control the heat transfer, and thus control the energy supply to and from the building. Therefore, there is a need for a device to control automatically the heat flux and thus to conserve energy.
The invention disclosed here makes it possible to regulate heat transfer and is especially useful for windows of buildings or other solar systems. Because heat flow cannot be measured directly, because of the complexity of the heat transfer processes, and because it is the result of these transfer processes which is important, what is needed is a device that will determine whether the net heat flux is positive or negative (where positive is defined as heat flow from outside to inside). This should be done in such a way that the decision as to whether to open or close the thermal barrier is made for the real situation existing on the inside and outside, with respect to the heat transfer conditions occurring. I have invented a device to make such a measurement, and which can be used to then control the heat transfer blinds, automatically, if desired.